Browsing by Subject "toroidal magnet"
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Item Demonstration of a Prototype, High Field, Single Turn, Toroidal-Magnet System(1991-09) Werst, M.D.; Hsieh, K.T; Sledge, R.L; Weldon, W.F; Woodson, H.H.Very high toroidal magnetic fields have been produced using a single-turn magnet powered by homopolar generators (HPGs). A design goal of a 20 tesla confinement field has been met by the combination of a low impedance toroidal magnet, a high current, low voltage power supply, and the use of a high strength, high conductivity copper alloy. The Ignition Technology Demonstration (ITD) is a 1/16 scale prototype of the proposed full-scale IGNITEX (Ignition Experiment) toroidal field (TF) magnet. Stresses and temperatures reached in the prototype TF magnet are representative of those that would be experienced in a 1.5-m major radius magnet with a 5 s flat top current profile. Synchronized, parallel operation of multiple homopolar generators into a single-turn toroidal magnet has been realized. The prototype TF magnet has produced toroidal magnetic fields up to 18.1 T on-axis with liquid nitrogen (LN2) precooling and axial preloading of the magnet. Room temperature operation of the magnet has produced on-axis fields up to 11.5 T and with LN2 precooling only, up to 15.4 T. Peak current from the HPG system for the 18.1 T test was 8.14 MA with an open circuit voltage of only 49 V. Generator synchronization is achieved by six, 1.5 MA rated, closing switches with a maximum jitter of 10 μs. A peak current density in the inner leg region of the TF magnet of 750 MA/m2 was experienced during the 18.1 T test. Peak temperature in the inner leg region for this test was measured to be 135°C. The description of the ITD experiment, operational experience, and test results are presented.Item High Current Transmission and Switching System for a Prototype, 20 Tesla, Toroidal Magnet(1991-09) Sledge, R.L.; Hsieh, K.T; Weldon, W.F; Werst, M.D.The Ignition Technology Demonstration (ITD) is a 0.06 scale prototype toroidal field magnet of the proposed full-scale IGNITEX (Ignition Experiment) tokamak. The goal of ITD is to achieve an on-axis magnetic confinement field of 20 T while demonstrating the magnet's ability to withstand high magnetic and thermal stresses [1,2]. To accomplish this task, a peak current of 9 MA must be transferred from six balanced homopolar generator (HPG)/busbar circuits to the liquid nitrogen (LN2) cooled magnet. HPGs are well suited for operation of single-turn coils because they are inherently high current, low voltage machines which can inertially store the energy required for a pulsed discharge. To date the system has delivered pulses of up to 8.14 MA to the toroidal magnet, producing an onaxis field of 18.1 T. In order to properly synchronize current transfer, an explosive closing switch is employed for each of the six independent HPG/busbar circuits. The switches operate by explosively driving a scalloped copper ring into a tapered annular gap made up of two copper alloy rings. With a jitter time of 10 μs, parallel circuit synchronization is better than 0.03% relative to the current rise time. The excellent performance of the switches during discharges of up to 8.14 MA is attributed to several design features which assure proper current distribution. Busbar design considerations have included electromagnetic loading, thermal gradients and magnet preloading effects. The switches and busbars have successfully operated at 82% of their rated action of 1.24 x 1011A2s per switch. Description of the ITD busbar/switching system, design improvements, and operational experience are presented.